A. Field of the Invention
The present invention relates generally to the communications field, and, more particularly to a hybrid polishing apparatus for polishing fiber optic cable connectors and method of polishing the same.
B. Description of the Related Art
Interconnection devices are used to join a fiber optic cable to another fiber optic cable or a fiber optic component. The most common interconnection device is the connector. Types of fiber optic cable connectors are as various as the applications in which they are used. Different connector types have different characteristics, advantages, disadvantages, and performance parameters. However, all fiber optic cable connectors consist of the same four basic components.
The fiber optic cable mounts inside a first component called the ferrule. The ferrule is a long thin cylinder that is bored through the center at a diameter that is slightly larger than the diameter of the cladding of the fiber optic cable. The end of the fiber optic cable is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but may also be constructed of plastic.
A second component, the connector body or connector housing, holds the ferrule. The connector body is usually constructed of ceramic, metal, or plastic and includes one or more assembled pieces which hold the fiber optic cable in place. The details of connector body assemblies vary among connectors, but bonding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip in a coupling device, described below.
The third component, the cable, attaches to the connector body, and acts as a point of entry for the fiber optic cable. Typically, a strain-relief boot is added over the junction between the cable and the connector body to provide extra strength to the junction.
Most fiber optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device (the fourth component), such as an alignment sleeve, is used to mate the connectors.
High loss optical connections limit the length and quality of fiber systems. Reflections created at the fiber optic cable connector can travel back towards the light transmitter and disrupt laser modulation, resulting in signal distortion. The goal of all connectors is low light loss and minimal back reflection.
The primary factors affecting the loss and reflective characteristics of a fiber optic cable connector are the fiber coupling alignment, and the contour of surface geometry of the end face of the optical fiber. The fiber optic cable must be aligned in a coupling device with minimum lateral and angular misalignment for maximum light transmission. The surface fiber end face must be free of scratches and pits for minimum reflection. The curvature and angle of the fiber and the connector's ferrule end surfaces must be of a magnitude that ensures physical contact and minimal back reflectance.
The final step in the termination of a fiber optic cable connector onto an optical fiber is the polishing of the fiber end face. Originally, this procedure was manually accomplished. A connector was placed in a polishing fixture so that its ferrule was slightly protruding from the fixture base surface. The fixture was then repetitively moved across an abrasive polishing film which removed fiber material until the desired scratch-free surface was attained. This procedure was time consuming and sensitive to the operator's individual touch.
Machines have been developed to automate the polishing process. While providing obvious advantages over manual polishing, conventional polishing machines have significant shortcomings regarding various steps in the polishing process. Conventional polishing machines are dependent upon the fiber optic cable connector's interlocking hardware for mounting onto the polishing work fixture. This limits the usefulness of a single work fixture for multiple connector styles. Currently, there are a multitude of connector styles, including SMA connectors, ST connectors, biconic connectors, FC connectors, D4 connectors, HMS-10 connectors (also known as Diamond connectors), SC connectors, LC connectors, fiber distributed data interface (FDDI) connectors, ESCON connectors, and EC/RACE connectors.
Increased labor and maintenance costs have necessitated a reduction in the time required to polish a fiber optic connector. The conventional polishing procedure involves multiple steps including the polishing of connectors on several types of polishing films. Minimizing these steps can greatly save time in the polishing operation.
Depending upon the application, some connectors require the fiber end face to be polished with a flat surface, other connectors require the fiber end face to be polished with an angled flat surface (preferably six-degree and eight-degree angles), while other connectors require the fiber end face to be polished with a conical end face. Moreover, the ferrules used in different connectors have different hardnesses. Thus, different connectors need to be polished at different angles with polishing surfaces and films having different hardnesses.
Conventional polishing machines use a single polishing surface and film, and thus, can only polish one type of connector at a time. Since different fiber optic cable connectors require fiber contact with different grits of polishing films and polishing surfaces, a machine with a single polishing surface and film will require the operator to change these surfaces and films several times during the complete process. Connectors having angled and conical fiber end faces further complicate the procedure because angled fixtures and different polishing pad hardnesses are required.
Using a single polishing pad and a variety of polishing films creates the potential for contamination from one connector type to another connector type. If the polishing film for one connector type contaminates the polishing pad (i.e., the pad is not sufficiently cleaned between connector polishing operations), there exists the potential for scratching a fiber end face of a connector. This is particularly true if the polishing film used for a connector having a ferrule with a hard material contaminates the polishing film used for connector having a ferrule with a softer material.
Furthermore, during a polishing operation, typically the connector moves on or traces a polishing pad in a pattern so that the connector never moves across the same portion of the polishing pad. Occasionally, however, a connector traverses over the same portion of the polishing pad. When this occurs, a connector trace overlap occurs. If connector trace overlap occurs, particulates of the hard connector ferrule may contaminate or mix with the polishing film or slurry and potentially scratch the relatively softer fiber end face.
Certain applications require a variety of fiber optic cable connectors to be used with a specific piece of fiber optic communications equipment. It is desirous to polish a complete set of connectors for a specific piece of fiber optic communications equipment with a single polishing apparatus. Unfortunately, with conventional polishing machines, an operator would have to polish a batch of one type of connector used in the set, and then change the polishing surface and film for the other connector types to be polished. Such a procedure is costly, time consuming, and may result in cross-contamination of polishing films between connectors.
Thus, there is a need in the art to for a polishing apparatus and method that polishes a variety of fiber optic cable connectors, having a variety of fiber end faces, eliminates the potential for contamination, reduces polishing process steps, and saves labor and maintenance costs.